Low and high fire control for liquid fuel burners



Oct. 28, 1947. ARNHYM 2,429,739

LOW AND HIGH FIRE CONTROL FOR LIQUID FUEL BURNERS Original Filed Nov. 6.1944

INVENTOR.

ATTORNEY.

Patented Oct. 28, 1947 I L ID E BURNERS I Albert-A. Arnhym; sun Diego, Calif., assignor to Solar Aircraft Company, San'Diego, Calif., acorporation *otcalifornia r I i r f Original apaicaan'mmbe; c, 1944,.sei-ni 'No.

562,238, Divided and this application Decemher 4 1945,5erlal'No, 632,773

This invention relates to heaters utilizing liquid fuel. suchas alcohol.

This application is a division of my copending 1944, and entitled l-leater."

An object of the invention is to provide a applicationSerial No. 562,236, filed November 6,

V rugged, reliable and emcient portable-heater.

Another object is to provide an alcohol heater than'can be quickly started and stopped and is largely automatic in operation.

Other specific objects and features oi the in- 2- Claims. (c1. .158-2 8) it' to open one or both of the electromagnetic Referring nowcto the drawiner e v 2 I Fig. 1 is a view looking into the Fig.2 is a detail view of the fuel inlet to the combustion chamber;

Fig. :3 is a schematic diagram operation of the heater.

vention will become apparent from theldetailed I description to follow of ap'articular embodiment of the invention; a J

Essentially, the heater of the present invention consists of a self-contained unit of generally cylindrical dimensions containinga combustion chamber, a, built-in fuel tank and fuel control devices for making the heater largely automatic in operation. The combustion chamber comprises a vertical chamber that is open at the top and closed ,at'the bottom and contains an upwardly extending re-entrant tube having air apertures in its side walls for delivering combus tion air. The fuel is introduced into the bottom of the combustion chamber and ignited'at the point of introduction. During periods when little or no heat is required, only a small amount of fuel'is admitted .which bums with a small fiame at the point of introduction and maintains a thermocouple heated, therthermocouple supplying'current for the control of magnetic valves in thefuelline. f

Preferably there are two valves connected in parallel in the fuel line, one of which is maintained openwhenever the thermocouple is energized an'd'passes a small stream of fuel sufllcient onlyto maintain thepilot flame. The othermasnetic :valve may be connected to a control switch or a thermostaticv switch solthat it is openonly' when the switch is closed. This second valve ad:-

mits a larger stream of fuel which overflows into the'bottom part ofthe combustion chamber and produces a fiame which more or less fills the chamber; s1

A particular feature of the invention is the use of a 'standpipe in the fuel linevbetween the elecrotion, there being a throat portion 2! of conical shape interconnecting the larger diameter lower' Referring to the drawing, the heater therein depicted comprises an outer cylindrical wall Ill of sheetmetal and an inner generally cylindrical wall ll positioned within the wall l0 and offset with respect to the axis of the latter. The inner wall ll hasa slight taper being smaller at the ,top than at the bottom for a purpose to be explained later. An intermediate horizontal partition wall it is also provided between the walls ,HI and II .and

secured'to them in fluid-tight relation to define;

a fuel reservoir l4. The-space belowthe partition wall [3 and exterior of the wall H is largely empty except for the fuel supply and control equipment which will be described later. A ball I! may be secured to the outer wall ill for convenience in handling. t r

The combustion chamber of the heater is positioned within and thermally insulated from the wall H. Thus an inner wall 20 defines the combustion chamber proper. It is of generally cylindrical shape but the upper section thereof is of somewhat smaller diameter than the lower secportion with the upper'small diameter portion.

At the lower end the wall 20 is flared inwardly V at an angle as indicated at 22 and joined as by welding to the lower end of an air supply tube 23, the latter having a lower end portion 24 of substantially the same diameter as the.neckof y theinwardlyflared portion 22 of the wall 20 but 1 j having an upper portion '25 of substantially smaller diameter. The large and smallsections magnetic valves -andj a master manual valve,

which standpipe is normally filled with fuel so that when the mastervalve is opened to start the heater, -'a substantial quantity offuel flows from'the standpipe intothe bottom of the com bustion chamb'er to immediately generate sufficient heat to energize the thermocouple and cause 7 the upperend of the air tube'23 which is located approximately at the upper end of zone 2| of the wall 20. 7

the transition bottom of a heater in' accordance with the invention;

illustrating the,

the wall 88 by a plurality of brackets 8|, these brackets also serving to maintain the proper spaced relation between walls 28' and 88. The wall 80 has an outwardly flared portionllla at its lower end which is connected by a bracket 82 to the wall l0, this bracket serving to support the wall 88 and everything therewithin in proper vertical position with respect to the; wall H.

In operation, as will be described later, there is quite a rapid flow of air upwardly through the annular passage 83 between the walls 20 and 88 which maintains the wall 88 at a substantially lower temperature than the wall 28. to maintain the inner wall ll of the fuel tank I4 at a sufllciently low temperature, thermal insulation is provided between the walls 38 and I I. This insulation may consist of an, inner layer 85 of some fire-resistant thermal insulating material, such as asbestos, and an outer layer 38 of some material, such as rock wool having a higher insulating efficiency than the inner wall 35. The use of a different material for insulation 38 is permissible because of the fact that it is not exposed to as high temperatures as is the layer 35.

Fuel is introduced into the annular trough 40 defined by the flared walls 22 and 28 through a fuel pipe 4| which connects to a pilot tube 42 of somewhat larger diameter. The upper end of the pilot tube 42 extends through the wall 22 in a fluid-tight relation with respect thereto. A thermocouple 44 is mounted on the wall 28 with its inner end projecting through the wall into position immediately above the pilot tube 42 so that it is heated by the pilot flame.

Referring to the bottomview of Fig. 1, fuel flows from the bottom of the tank through a fitting 48 and a tube 48 and through a filter 41 into a control unit 48, and from the latter through a tube 48 and a cock 58 to the tube 4 I. I

The control unit 48 contains a float bowl and a pair of electromagnetic valves. Referring to the schematic diagram of Fig. 3, the float bowl 5| is indicated as containing a float 52 actuating a needle valve 53 through which fuel enters from the filter 41. The float valve maintains a constant level of fuel in the float bowl 5| irrespective of the height of the fuel in the main tank i4.

From the bottom of the float bowl 52, fuel fiows into a chamber 54,'from which it can escape only through one or both of the tubes 55 and 55. Flow into the tube '55 is. controlled by an electromagnetic valve 51 and flow into tube 58 is controlled by anelectromagnetic valve 58.

As shown in Fig. 3, auxiliary manual valves 58 and 88 are shown in the tubes 55 and 58, respectlvely, for controlling the rate of flow through those tubes when the electromagnetic valves are open. However, these valves 58 and 88 might be replaced by fixed flow orifices, if desired. 7

The two tubes 55 and 58 merge into the single I tube 49 which has connected thereto a standpipe 8| having a small vent aperture- 82 in its upper end. Fuel flows from the tube 49 through the .cock 58, when the latter is open, and through the tube 4| to the pilot tube 42.

The electromagnetic valves 51 and 58 are actu-' ated by current from the thermocouple 44. Valve 51 is permanently connected to the thermocouple so that itis open-so long as the thermocouple is heated, and it controls the flow of fuel to maintain the pilot flame when no heat is desired. The

However,

'4 other electromagnetic valve 58 admits a larger quantity of fuel to the burner when heat is desired, and it is connected to the thermocouple 44 in series with a thermostatic switch 84, although.

a manual control switch can be used if desired. When a thermostatic switch is employed, it is preferably mounted in the coolest part of. the device so that it will be responsive to the temperature of the air entering the heater and will be relatively non-responsive to the heat generated in e the combustion chamber.

, Operation is started by opening the valve 58.

'Forreasons that will be explained later, the standpipe 8| will be filledwith fuel to the level of the liquid in the float bowl-5l prior to opening of the valve 58 so that immediately following opening of the valve, the fuel in the standpipe drains quickly into the annular trough 48 in'theu bottom of the combustion chamberand may be ignited with a match. The fire screen .18. may

have a hole 18a through which a matchmay be entered on a holder. the flint and steel variety may be built into the heater, if desired.

As previously indicated, the fuel is preferably f alcohol which ignites readily and quickly warms the walls of the combustion chamber and 'the inner end of the thermocouple 44. The dimen- 4 sions of the standpipe 6! are. so chosen that the amount of fuel initially supplied from the standpipe is sufiicient to heat the thermocouple 44 .to i

a point where it generates sufiicient current to; open the magnetic relays 51 and 58. Fuel there- 4 upon flows immediately through the pipe 55 in asmall quantity sufficient to maintain a pilot flame so that the level of the liquid in the standpipe will not rise much above the level of the inlet tube 42. So long as fuel is supplied only through the pipe 55, it'does not escape from the inlet tube 42 but vaporizes within the tube and burns with a flame immediately thereabove to heat the thermocouple 44. The height of the liquid is automatically regulated since if it tends to'rise in the inlet tube 42, it is heated more by the heme and evaporated faster so that the level drops until a I 7 position of equilibrium is reached.

If the thermostatic switch 64 or a manual switch in place thereof is closed, the circuit will also be completed for opening the magnetic valve 58 to f .permit a larger quantity of fuel to flow through the pipe 56. In addition to the flow through the pipe 55, the quantity supplied when the valve 58 is open is usually sufficient to overflow the inlet" tube 42 into the trough 50 where it ishapidly vaporized and burned.

The main flow of fuel through tube 58 can be interrupted by the action of the switch 64 which deenergizes and closes the valve 58 without interrupting the small flow of fuel through pipe 55 to Alternatively, a lighter oflevel of the liquid in the float bowl When it is desired to shut the heater down completely, the valve 50 is again closed. This immediately stops all flow of fuel to the combustion chamber and the flame therein is soon extinguished. Immediately upon closure of the valve 50, the fuel flowing through pipe 55 or through pipes 55 and 56 enters the standpipe 6! up to the This'occurs before the thermocouple 44 cools oif enough to de-energize the valves 51 and 58. The liquid remains in the standpipe Bl ready to charge the combustion chamber and start the operation the next time the valve 50 is opened.

A heater in accordance with the invention having a fuel capacity of live gallons is capable of supplying 15,000 B. t. u. per hour for approximately twenty-three hours and supplying 10,000 B. t. u. per hour for approximately thirty-four hours. The pilot flame is required to generate approximately 300 B. t. u. per hour in order to insure that the flame will be of sufficient size not to be blown out and to heat the thermocouple to the required temperature.

It is found that the supply of combustion air through the holes 21 and 28 in the central tube 23 provides very complete combustion. Tests indicate that the maximum quantity of carbon monoxide present in the exhaust gases from the heater is approximately 0.002% which is well below the safety limit.

The flared walls at the lower end of the combus tion chamber, in addition to defining the annular trough 40, define an enlarged central opening to the tube 25 and an enlarged annular opening leading to the air passage 33. The particularly free flow of air into the tube 23 and out through the holes 21 and 28 therein insures an ample supply of air for complete combustion. The rapid flow of air through the annular passage 33 is highly desirable in that it helps to maintain the outer wall 30 at a low temperature and reduces the temperature of the inner wall of the fuel tank. It also insures the supply of a relatively large amount of moderately heated air from the heater rather than a small amount of more intensely heated air.

In operation, when the main valve 60' is opened, the fuel flows over the top of the pilot tube 42 into the annular trough of the combustion chamber and starts burning on its surface. Shortly thereafter, as the combustion chamber warms up and draft is created in the outer duct 33 and the injection column 23, the jet action previously mentioned is started. Thereafter, the fluid fuel vaporizes more readily, and after the device has been in operation for a short time, the flame leaves the surface of the fuel entirely and combustion commences at the air jets issuing from the orifices 21 and 28, the lower portion of the combustion chamber below the lowest orifice 2! being then filled with vaporized fuel. The rate of vaporization becomes faster as the temperature rises and the pressure Within the combustion 6 chamber is reduced. The fuel level in the annular trough then gradually lowers to establish an equilibrium where the rate of vaporization equals the rate of liquid fuel supplied,

Although for the purpose of explaining the invention a specific embodiment thereof has been described in considerable detail, various departures from the exact construction can be made without departing from the invention which is to be limited onlyto the extent set forth in the appended claims.

I claim:

1. A liquid fuel combustion device comprising: a combustion chamber, the lower portion of which is liquid-tight for the retention of liquid fuel; a fuel supply line entering said combustion chamber; a source of fuel at a head above the bottom of said combustion chamber; first control valve. means positioned in said fuel line betwee 1 said source and said combustion chamber; a standpipe connected to said fuel line between said first valve means and said combustion chamber; a starting valve in said fuel line between said standpipe and said combustion chamber; means for electrically operating said first valve to open it including a thermocouple positioned in said combustion chamber for supplying current to open said first valve, said standpipe being so'proportioned as to normally supply enough fuel to said combustion chamber followin opening of said second valveto develop sufiicient heat to en-' 'ergize said thermocouple and open said first valve.

chamber for supplying a larger quantity of fuel thereto; and circuit means including a separate control switch for connecting said last-mentioned valve to said thermocouple.

" ALBERT A. ARNHYM.

REFERENCES CITED The following references are of record in the file of this patent:

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